UTR (Urotensin-ll receptor) is a recently de-orphanized GPCR, previously known as GPR14 that binds the peptide, Urotensin-ll (U-ll). U-ll is a potent vasoconstrictor, as well as a mitogenic and hypertrophic agent for vascular smooth muscle cells and cardiomyocytes. Consequently, the UII-UTR signaling pathway has been implicated in different cardiovascular pathologies, such as pulmonary arterial hypertension (PAH) and chronic heart failure. But the role of U-ll remains controversial, since it also causes vasodilation in some vessels under certain conditions. It has been postulated that U-ll may be involved in maintaining vascular tone in normal individuals, whereas in cardiovascular disease, endothelial dysfunction may result in an undesirable imbalance between the contractile and dilatory functions of U-ll. Although circumstantial evidence supporting this notion is slowly beginning to emerge, medical and research communities clearly recognize a critical need to develop specific reagents that will allow pharmacological blockade of U-ll. We have recently identified a potent, non-peptidic small molecule inhibitor series that specifically antagonizes biological actions of U-ll and UTR. In this SBIR Phase I proposal, we aim to evaluate further this series to optimize its drug-like characteristics. Phase I objectives are: 1) to evaluate the receptor potency, mechanism of action, and selectivity of lead compound series using well-defined in vitro assays. Functional antagonism (IC50 and pA2 determinations) of this series of antagonists against recombinant human UTR will be assessed by comparing compound potencies in membrane-, and cell-based assays. Receptor selectivity will be determined by testing lead compound series against other GPCRs; 2) to use lead compound(s) to test the hypothesis that urotensin-ll plays a causal role in an animal model of pulmonary hypertension. We will determine if the U-II/UTR system plays a role in mediating central and/or peripheral hemodynamic changes following exposure to hypoxia (10% O2) in the rat. And 3) to assess functional antagonism of lead compounds against urotensin ll-induced contraction of human pulmonary arteries. Successful completion of this Phase I SBIR proposal will provide us with critical information needed to select a novel drug candidate for further preclinical development. A UTR selective antagonist may represent a novel pharmacological approach to treat serious, life-threatening cardiovascular diseases.